1. Field of the Invention
The present invention relates to a DC-AC converter which generates alternating current for a load with an inductive component from direct current voltage where the frequency of the generated alternating voltage is in the neighborhood of from about 10 to 100 kH and can be about 30 kH.
2. Brief Description of the Background of the Invention Including Prior Art
DC-AC converters are known (Electronique Industrielle, Issue 50, Jan. 4, 1983, pp. 35-41) where a direct current voltage is applied to a so-called half bridge with two power transistors connected in series. The power transistors are gated alternatingly conducting and generate at their connection point an alternating voltage for the load. Theoretically, the first transistor should be switched off at a certain point in time, and the second transistor should be switched on at the same point in time. The inductive component of the load however, does not allow a sudden current interruption. On the other hand, the transistors would be endangered if they are both simultaneously conducting for a short time. Because of the tolerances and the depletion and emptying times of the transistors, such an exact circuit is possible only with complicated driver circuits provided as microprocessors.
Therefore it is known to provide a rest time between such successive conducting phases of the two transistors to provide safety, and during this rest time the two transistors are nonconducting. This assures that the two transistors cannot be conducting simultaneously. In order to allow the required current flow during this rest time, the transistors have poled diodes connected in parallel opposite to their collector-emitter sections, and the diodes pass the current during the rest time for a short time. In each case a capacitor is disposed in parallel to the diodes which limits the steepness of slopes of the generated alternating current.
The two transistors are in this case alternatingly in counter cycles conductingly gates and blocked by the windings of a transformer. An additional driver circuit has to be coordinated to the transformer for this purpose, where the driver circuit effects this gating and blocking of the transistors. Such a driver circuit requires additional expenditures for switching procedures and energy. For example, a driver circuit can be an additional stage which is fed with a separate operating voltage.